As is well known, seat reclining devices are utilized in seats of automotive vehicles for adjusting an angular position of a seat back relative to a seat cushion. In recent years, there have been proposed and developed various seat reclining devices, in which a speed of an electric motor, serving as an actuator, is reduced at a high reduction ratio by a planetary reduction gear mechanism (an eccentric-drive speed reducer) for angular adjustment of a seat back relative to a seat cushion.
Such eccentric-drive equipped seat reclining devices have been disclosed in Japanese Patent Provisional Publication No. 06-40277 (hereinafter is referred to as “JP06-040277”), corresponding to U.S. Pat. No. 5,308,294, issued on May 3, 1994 and Japanese Patent Provisional Publication No. 2006-340872 (hereinafter is referred to as “JP2006-340872”). In the eccentric-drive equipped automobile seat hinge joint disclosed in JP06-040277, a first component (a first leaf) fixedly connected to a seat cushion and a second component (a second leaf) fixedly connected to a seat back are pivotally connected to each other via a relative-angle adjusting mechanism. The relative-angle adjusting mechanism is comprised of a spur gear, which is an integral part of the first leaf and can be obtained by stamping and has external teeth formed on the outer periphery, and a substantially annular internal gear, which is an integral part of the second leaf and can be obtained by stamping and has internal teeth. The spur gear has one fewer external teeth than the number of internal teeth on the annular internal gear, and the external teeth of the spur gear mates in a certain way with the internal teeth of the internal gear, so as to permit the spur gear and the internal gear to roll along each other. Also, a pair of wedge-shaped members and a centering element are accommodated in an annular eccentric space defined between the inner peripheral surface of the first leaf and the outer peripheral surface of a bush (an outer sleeve), which bush is press-fitted to the second leaf and surrounds a tubular actuating inner sleeve (serving as a driving member of the relative-angle adjusting mechanism) such that the actuating inner sleeve is rotatable relative to the second leaf. Also provided is a circular-arc spring (a torsion spring) whose first leg bears against the radially-wider end portion of one of the two wedge-shaped members and whose second leg bears against the radially-wider end portion of the other wedge-shaped member, such that the radially-narrower two opposing end portions of the wedge-shaped members are forced toward each other.
In the seat reclining device disclosed in JP2006-340872, an external gear and a base plate of the seat cushion side are press-fitted to each other. On the other hand, the outer peripheries of an internal gear and the base plate are retained or held by means of a holder ring, while superposing the internal gear on the base plate. The outside face of the base plate, produced by stamping, is formed with embossed portions, which protrude in one axial direction of a pivot axis of a seat-cushion side mounting arm and a seat-back side mounting arm and by which the base plate is fixedly connected to the seat-cushion side mounting arm. The outside face of the internal gear, produced by stamping, is also formed with embossed portions, which protrude in the opposite axial direction of the pivot axis and by which the internal gear is fixedly connected to the seat-back side mounting arm. In the case of the seat reclining device of JP2006-340872, only a pair of wedge-shaped members is installed in an annular eccentric space without a centering element (a guide plate). Also provide is a metal bearing press-fitted to the inner peripheral surface of the external gear.